The present invention relates to electrical circuits, and specifically concerns drivers for producing high-current signals from low-level logic inputs.
Driver circuits are commonly used to increase the level of binary logic signals for driving long lines or multiple loads. Frequently, a removable plug is inserted between the driver output and the loads which it drives. In such applications, there is always a significant possibility that the driver output may become accidentally shorted during handling or testing. Unless such fault conditions are provided for, the driver will burn out from excessive power dissipation.
Common practice in the past has been to select an output transistor with a sufficiently high power rating to withstand accidental short circuits across the driver-circuit output terminals. Since the short-circuit dissipation is normally at least several times the normal full-load dissipation, this practice leads to increased cost and size. It usually requires, for example, that the output transistor be in a separate package from the remainder of the driver circuit. The art has recognized the broad concept of adding control circuitry to shut down an output transistor under overload conditions. But such circuitry has always sensed the output itself, which entails degradation of the output signal, complex sensor circuits, and/or imprecise dissipation control.